Yang et al. Nanoscale Research Letters (2015) 10:222 DOI 10.1186/s11671-015-0932-1

NANO EXPRESS Open Access

Flexible conducting polymer/reduced grapheneoxide films: synthesis, characterization, andelectrochemical performanceWenyao Yang, Yuetao Zhao, Xin He, Yan Chen, Jianhua Xu*, Shibin Li, Yajie Yang and Yadong Jiang

Abstract

In this paper, we demonstrate the preparation of a flexible poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonate)/reduced graphene oxide (PEDOT-PSS/RGO) film with a layered structure via a simple vacuum filtered method as a highperformance electrochemical electrode. The PEDOT-PSS/RGO films are characterized by scanning electron microscopy(SEM), X-ray diffraction, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectrometry. The resultsindicate that a layer-ordered structure is constructed in this nanocomposite during the vacuum filtering process.The electrochemical performances of the flexible films are characterized by electrochemical impedance spectroscopy,cyclic voltammetry, and galvanostatic charge/discharge. The results reveal that a 193.7 F/g highly specific capacitanceof nanocomposite film is achieved at a current density of 500 mA/g. This flexible and self-supporting nanocompositefilm exhibits excellent cycling stability, and the capacity retention is 90.6 % after 1000 cycles, which shows promisingapplication as high-performance electrode materials for flexible energy-storage devices.

Keywords: Flexible; PEDOT-PSS; Reduced graphene oxide; Supercapacitor

BackgroundSupercapacitors, also called electrochemical capacitors,are one of the important energy-storage devices with fastcharging/discharging, high power density, high energydensity, and long cycle life, which could fill the gap be-tween the conventional capacitors and the batteries [1,2]. Conductive polymers can store charges not onlythrough pseudocapacitances but also in the electricaldouble-layer capacitances (EDLCs). The pseudocapaci-tance is due to faradic charge transfer, while the EDLCscould store energy by an ion adsorption-desorptionprocess in the double electrical layer at the electrode/electrolyte interfaces [3, 4]. As a result, the conductivepolymer electrodes present higher specific capacitancethan that of pure carbon-based capacitors with EDLCs[5]. One of the most significant problems is that pureconducting polymers are usually mechanically weak orbrittle, leading to poor cycling stability during the longcycle charge/discharge process [6, 7]. Coupling conductive

* Correspondence: jianhuaxu215@163.comState Key Laboratory of Electronic Thin Films and Integrated Devices, Schoolof Optoelectronic Information, University of Electronic Science andTechnology of China (UESTC), Chengdu 610054, People’s Republic of China

© 2015 Yang et al.; licensee Springer. This is anAttribution License (http://creativecommons.orin any medium, provided the original work is p

polymers to a carbon material has been proven to be aneffective approach to overcome this problem [8, 9]. Thereduced graphene oxide (RGO), which exhibits high per-formance of electrical and electrochemical activity com-bined with favorable mechanical strength, can be obtainedby reducing graphene oxide (GO) through chemical treat-ment [10, 11]. The nanocomposites, based on conduct-ing polymer and RGO, exhibit chemical stability andideal capacitive behavior when they are used as elec-trode materials [12–14].Due to the fast development of flexible electronics, the

requirement for high-performance flexible energy-storagedevices is bursting. Furthermore, a self-supporting andcollector-free supercapacitor electrode with large energydensity and great mechanical strength is an importantcomponent for a flexible energy-storage device. Recently,much attention has been focused on the conductingpolymer poly (3,4-ethylenedioxythiophene)-poly (styre-nesulfonate) (PEDOT-PSS), which was used as a flexibleelectrode due to high conductivity and flexible process-ability [15–17].In this paper, we demonstrate the preparation of flex-

ible and self-supporting PEDOT-PSS/RGO films as an

Open Access article distributed under the terms of the Creative Commonsg/licenses/by/4.0), which permits unrestricted use, distribution, and reproductionroperly credited.

Yang et al. Nanoscale Research Letters (2015) 10:222 Page 2 of 7

electrochemical electrode via a simple vacuum filtrationmethod. In the first step, the GO was prepared by amodified Hummer’s method, and the RGO was obtainedby a following hydrazine reduction treatment. Then, thePEDOT-PSS/RGO nanocomposites were prepared by anin situ solution polymerization. The PEDOT-PSS waspolymerized on the surfaces of RGO sheets, and asandwich-like PEDOT-PSS/RGO structure was formed.After that, the self-supporting nanocomposite films witha layer-by-layer structure were prepared by vacuum- fil-tered method. The PEDOT-PSS/RGO nanocompositefilms showed better electrochemical properties comparedwith the pure RGO and PEDOT-PSS films. The combin-ation of flexibility and electrochemical activity makes thisself-supporting nanocomposite film attractive for applica-tions in organic and flexible electrode materials.

MethodsMaterialsThree, 4-ethylenedioxythiophene (EDOT) was purchasedfrom Bayer Company (Leverkusen, Germany). Graphiteflakes (Grade 3061) and Polystyrenesulfonate (PSS 25 %)were bought from Sigma-Aldrich (St. Louis., MO, USA).Cation exchange resin (001 × 7) and anion exchangeresin (201 × 7) were purchased from Bohong Company(Tianjin, China). Ammonium persulphate ((NH4)2S2O8,98 %), Mohr’s salt ((NH4)2Fe(SO4)2 · 6H2O, 99 %) andethanol (C2H6O, 99.5 %) were purchased from KelongChemicals (Chengdu, China).

Preparation of PEDOT-PSS/RGO self-supporting filmsThe RGO was synthesized from graphite flakes by themodified Hummer’s method and hydrazine reductionmethod [18, 19]. Deionized water and ethanol-mixed so-lution (volume ratio 1:1) was used to improve the solu-bility of EDOT. 100 mg RGO was dispersed in 200-mLmixture solution by sonicating for at least 2 h. In situpolymerization solution of PEDOT-PSS/RGO was pre-pared by introducing 1.4 mmol PSS and 0.7 mmolEDOT into the 200-mL RGO dispersion. This in situpolymerization solution was vigorously stirred and keptat 5 °C. Then, 1.4 mmol ammonium persulphate and0.0014 mmol Mohr’s salt dissolved in 100 mL deionizedwater were added slowly while stirring overnight. Finally,the inorganic impurities in the final PEDOT-PSS/RGOdispersion were removed by 001 × 7 cation-exchangeresin and 201 × 7 anion- exchange resin.The PEDOT-PSS/RGO dispersion was sonicated for

2 h and vacuum filtered by PTFE filter membranes (poresize 0.22 μm, diam. 47 mm). Then the films were washedwith ethanol and dried at 60 °C for 24 h in vacuum.After that, the dried films were stabilized at 235 °C invacuum for 30 min and then peeled off from the filter toform self-supporting films.

The PEDOT-PSS/RGO self-supporting films synthe-sized from different mass ratios were labeled as PS/RGratio. The PS/RG 1:1 indicates that the mass ratio ofEDOT and RGO was 1:1. Meanwhile, the pure PEDOT-PSS and pure RGO self-supporting films were synthe-sized by a similar synthesis method mentioned above.

Characterization and electrochemical measurementsThe morphologies of PEDOT-PSS/RGO films were in-vestigated with S-4800 scanning electron microscopy(SEM). X-ray diffraction (XRD) patterns were performedon an X’Pert PRO diffractometer with Cu Ka radiation(λ = 0.154 nm). Raman spectra were characterized with aHoriba LabRAM HR system (633 nm laser). Fouriertransform infrared (FT-IR) spectra were characterizedwith a ThermoElectron Nicolet 6700 spectrophotometer.A CHI660D electrochemistry workstation was used tocharacterize the electrochemical performance of the sam-ples at ambient temperature. Electrochemical impedancespectroscopy (EIS), cyclic voltammetry (CV), and galvano-static charge/discharge (GCD) were performed with a 1-mol/L Na2SO4 aqueous electrolyte. The platinum foils andan Ag/AgCl electrode were used as counter and referenceelectrodes, respectively. All the measurements were per-formed at ambient temperature.

Results and discussionThe SEM images of pure RGO and PEDOT-PSS/RGOnanocomposite films are shown in Fig. 1. The changes ofthe microstructures of the films provide important infor-mation to reveal the strengthening mechanism of thenanocomposite films. The SEM image in Fig. 1a indicatesthat the pure RGO film is composed of a large quantity ofcurved nanosheets. As PEDOT-PSS/RGO nanocompositefilms (shown in Fig. 1b), a porous 3D network structurewith a few folds is presented. It is clear that the RGOnanosheets are homogeneously coated by PEDOT-PSS,indicating that PEDOT-PSS was successfully polymerizedon the surfaces of RGO nanosheets to form sandwich-like structures. The cross-section of PEDOT-PSS/RGOnanocomposite film (shown in Fig. 1c and d) present alayer-by-layer formation, which is probably caused bythe flow-assembly effect of RGO sheets during filtra-tion [20–22].Raman and FT-IR spectroscopy provide powerful tools

to further investigate the microstructure of composites.Fig. 2a shows the Raman spectra of pure RGO andPEDOT-PSS/RGO composite films. The Raman spectrumof RGO displays two typical bands centered at 1347 and1579 cm−1, corresponding to the D-band and G-band, re-spectively. The D-band indicates the increasing of the sp3

domains and the decrease of the in-plane sp2 domains.The G-band, due to the E2g mode, is closely related to thevibration of sp2-bonded carbon atoms in a 2D graphene

Fig. 2 (a) Raman spectra of pure RGO and PS/RG 1:1 films; (b) FT-IRspectra of RGO, and PS/RG 1:1 films

Fig. 1 SEM images of flexible films as follows: (a) pure RGO, (b) PS/RG 1:1 and (c, d) cross-section images of PS/RG 1:1

Yang et al. Nanoscale Research Letters (2015) 10:222 Page 3 of 7

layer [23, 24]. The Raman band of PEDOT-PSS/RGOcomposite films (shown in Fig. 2b) at 985 cm−1 is assignedto oxyethylene ring deformation. The band at 1123 cm−1

is originated from C-O-C deformation. The bands at1281 and 1363 cm−1 are originated from the Cα-Cα

inter-ring and Cβ-Cβ stretch, respectively. The bands at1432 and 1501 cm−1 are attributed to C = C symmetricstretch. The asymmetric Cα-Cβ bond is evidenced bythe presence of band at 1561 cm−1 [23, 25]. The seriesof bands indicates the successful formation of PEDOT-PSS/RGO nanocomposites.Figure 2b presents the FT-IR spectra of pure RGO and

PS/RG 1:1 composite films. The spectrum of RGO filmdisplays two peaks about at 1629 and 1089 cm−1, attrib-uting to the aromatic C = C and oxygenated bond C-C-O, respectively [26]. We conclude that the oxygenatedbond C-C-O arises from residual oxygen containingfunction groups in the RGO sheets, which improves thesolubility of RGO. From the FT-IR spectrum of PS/RG1:1, the spectrum contains peaks of C = C, C-C and C-O-C bonds in the thiophene ring at 1514, 1321, and1188 cm−1 [8]. The C-S bond in the thiophene ring is ev-idenced by the presence of bands at about 977, 919 and833 cm−1 [27]. Additionally, the bands at 1142 and1052 cm−1 are attributed to the S-O bond and S-phenylbond in PSS [28]. Moreover, the above-mentioned char-acteristic peaks of RGO are reflected in the spectrum ofthe PS/RG 1:1 film. However, the peak corresponding tothe aromatic C = C and oxygenated bonds C-C-O areblue-shifted to 1628 and 1080 cm−1, suggesting interac-tions between PEDOT-PSS backbone and RGO sheets[29]. Therefore, the series of bands in FT-IR spectra in-dicates the successful formation of PEDOT-PSS coatingson the surfaces of the RGO.

Fig. 4 Nyquist plots of varied films. Inset shows plots with enlarged scale

Yang et al. Nanoscale Research Letters (2015) 10:222 Page 4 of 7

Figure 3 shows the XRD patterns of pure PEDOT-PSS,pure RGO, and PEDOT-PSS/RGO nanocomposite filmswith different RGO contents. The broad peak of PEDOT-PSS pattern ranging from 16.4 to 30.9 ° is attributed toPEDOT-PSS [30]. The pure RGO, PS/RG 1:9, and PS/RG1:1 exhibits a small peak centered at 10.9 °. We concludethat this small peak arises from residual oxygen containingfunction groups in the RGO sheets, which improves thesolubility of RGO. However, this small peak disappears inPS/RG 9:1 probably due to the low mass ratio of RGO.Compared with pure RGO, the XRD pattern of thePEDOT-PSS/RGO nanocomposites exhibits a broad peakranging from 15 to 30 °, which is similar with RGO. Theintensity of the peaks increases a little, which is ascribedto the reflection of PEDOT-PSS. Therefore, the XRD pat-tern further confirms the formation of PEDOT-PSS coat-ings on the surfaces of the RGO, which is consistent withthat of the Raman investigations [31].The electrochemical performances of PEDOT-PSS/

RGO films were analyzed by using EIS, CV, GCD, andcycle-life tests. The Nyquist plots of pure PEDOT-PSS,pure RGO, and PEDOT-PSS/RGO nanocomposite filmswith different RGO contents are showed in Fig. 4. It canbe seen that all the plots exhibit the capacitive-type be-haviors. It is well known that the first interception of theplots at the Z’ axis represents the equivalent series resist-ance (ESR), and the diameter of the semicircle is as-cribed to the charge transfer resistance at the electrode/electrolyte interface [26]. As shown in Fig. 4, the ESR ofthe PEDOT-PSS, PS/RG 9:1, PS/RG 1:1, PS/RG 1:9, andRGO films are 2.56, 2.15, 1.62, 1.87, and 1.35 Ω, re-spectively. For the pure PEDOT-PSS and PS/RG 9:1films, the radii of the semicircles in the Nyquist plotare larger than PS/RG 1:1, displaying a small semicirclecharacterization in high frequency range. This result in-dicates that the charge transfer resistance of PS/RG 1:1film was lower than that of pure PEDOT-PSS and PS/

Fig. 3 XRD patterns of RGO, PEDOT-PSS, and composite films

RG 9:1 films. This might be due to the fact that the ag-glomeration of PEDOT-PSS films during the charge/discharge process decreased the effective surface areabetween the electrolyte and electrodes. Meanwhile, theinconspicuous semicircles at high frequency of PS/GR1:9 and RGO films suggest that the interfacial chargetransfer resistance is significantly low due to the highelectrical conductivity of RGO [10]. The sloped portionclosed to 45 ° in these plots at low frequency is typicalof Warburg resistance, which is the result of the fre-quency dependence of ion transport or diffusion in theelectrolyte [32, 33]. The Warburg region of RGO, PS/RG1:9, and PS/RG1:1 films are smaller than that ofPEDOT-PSS or PS/RG 9:1 films, indicating that theshorter ion diffusion paths are formed during thecharge/discharge process. Hence, we deduce that themore contents of RGO in nanocompoistes, the lowerWarburg resistance is achieved in electrode materials.At the low frequency, all plots exhibit almost verticalstraight lines, especially those films with a high massratio of RGO, indicating that these nanocomposite filmsexhibited an ideal capacitive behavior during the energystorage process. This result also reveals that a low-resistance interface was formed between the PEDOT-PSSand RGO, which is suitable for fast adsorption and de-sorption of solution ions.Figure 5a shows the CV curves of composite films

within potential range from −0.2 to 0.8 V in a 1-MNa2SO4 electrolyte at a scan rate of 20 mV/s. It can beseen that the CV curves of all the films displayed an al-most rectangular shape, indicating the good capacitiveproperties of RGO and PEDOT-PSS nanocomposites. Itis clear that PEDOT-PSS/RGO films exhibit larger CVarea than that of pure PEDOT-PSS and pure RGO films,revealing higher charge-storage capability of nanocom-posites. It is well known that as an electrochemical cap-acitor electrode, the PEDOT-PSS/RGO nanocomposite

Fig. 5 (a) Cyclic voltammograms curves of varied films at a scanningspeed of 20 mV/s; (b) Galvanostatic charge to discharge curves of variedfilms at a current density of 500 mA/g

Yang et al. Nanoscale Research Letters (2015) 10:222 Page 5 of 7

films can afford both pseudo capacitance and EDLCsduring the electrochemical energy storage process. Theenhanced-charge storage capability is attributed to thewell dispersion of RGO in PEDOT-PSS, providing athree-dimensional net work for charge transmission.The highly specific surface area of RGO and high pseudocapacitance of conducting polymer lead to excellent cap-acitance performance of nanocomposite electrode. Asshown in Fig. 5a, the PS/RG 1:1 film shows the largestCV area corresponding to the highest specific capaci-tance, indicating the optimum contents of conductingpolymer in nanocomposites. Accordingly, the decreasingof conducting polymer contents in nanocomposites causeslesser contribution of pseudo capacitance, leading tosmaller CV area and specific capacitance. It needs to bementioned that the lower contents of RGO in a compositefilm will not hinder the conductive polymer from agglom-erating effectively during the charge/discharge process,leading to smaller specific capacitance. It has been foundthat a mass ratio of EDOT to RGO, about 1:1, was the

optimum proportion to prepare PEDOT-PSS/RGO nano-composites with excellent capacity performance. More-over, the Fig. 5a also suggests that the PEDOT-PSS/RGOfilm exhibits an excellent electrical synergistic effect, andlow contact resistance is formed between electrolyte andelectrodes.A comparison of capacitive performance was performed

using galvanostatic charge/discharge curves at a constantcurrent density of 500 mA/g, which is shown in Fig. 5b. Itis clearly seen that the shape of the charge/dischargecurves of varied films are closely triangular in shape, indi-cating a good reversibility during the charge/dischargeprocesses. The discharge times of the PEDOT-PSS/RGOnanocomposite films are longer than that of the purePEDOT-PSS and pure RGO films, suggesting the coatingof the PEDOT-PSS on the RGO surface greatly extendingthe discharge time. Moreover, the PS/RG 1:1 film showsthe longest charge/discharge time, indicating the largestspecific capacitance of these electrode films. The spe-cific capacitance can be calculated from the capacitanceequation:

Cm ¼ iΔtmΔV

Where the Cm, i, Δt, ΔV and m represent the specificcapacitance, discharge current, discharge time, dischargepotential window, and mass of nanocomposite films, re-spectively. According to the capacitance equation evalu-ated from the slopes of the discharge curves, the specificcapacitance of pure PEDOT-PSS, PS/RG 9:1, PS/RG 1:1,PS/RG 1:9, and pure RGO films are 106.3, 143.4, 193.7,129.2, and 81.8 F/g, respectively. The highly specific cap-acitance in PEDOT-PSS/RGO films results from thesynergetic effect between PEDOT-PSS and RGO, whichwas constructed with a layer-by-layer and porous struc-ture. This special structure also results in improvingelectrolyte-ion transfer efficiency and better frequencyperformance of electrode films during the charge/dis-charge process.The stability of different films as energy storage elec-

trodes was evaluated by charge/discharge cycling tests ata current density of 500 mA/g (Fig. 6). The pristine spe-cific capacitance of RGO is 81.8 F/g, and decreasesslightly to 79.5 F/g (97.2 % retention) after 1000 cycles.The specific capacitance loss of RGO film is small, and thecarbon nanomaterial shows excellent capacity-retentioncapability. In contrast, the PEDOT-PSS film shows higherspecific-capacitance loss than RGO film with poor cyclingperformance. The capacitance value of PEDOT-PSS filmdecreases from 106.3 to 98.4 F/g in the first 150 cycles(7.4 % loss) and decreases slightly to 96.8 F/g during thenext 150 cycles (1.5 % loss). An obvious decrease of spe-cific capacitance is observed after the 1000 cycles (40.5 %

Fig. 6 Cycling performances of varied films at a current density of500 mA/g

Yang et al. Nanoscale Research Letters (2015) 10:222 Page 6 of 7

loss), which is attributed to the poor mechanical cap-ability of conducting polymer during the charge/dis-charge process, especially at high current density. Thespecific capacitance of PS/RG 1:1 film can maintained90.6 % of initial capacitance (175.4 F/g) after 1000 cy-cles. Obviously, the addition of RGO into PEDOT-PSSimproves the mechanical performance of PEDOT-PSS,which results in a better cycling stability of conductingpolymer. The PS/RG 9:1 and PS/RG 1:9 films also presentbetter capacity retention performance than PEDOT-PSSfilm and keep 74.5 % (106.8 F/g) and 93.1 % (120.3 F/g) ofinitial specific capacitance over 1000 cycles, respectively. Itcan be estimated that, under the proper mass ratio ofRGO, more RGO in nanocomposites results in better cyc-lic stability of composite films. This result reveals that theRGO sheets provide a robust mechanical support forPEDOT-PSS, preventing conductive polymer from swell-ing and shrinking during the long-time charge/dischargeprocess. Therefore, it has been found that an optimumproportion of EDOT to RGO with 1:1 is better to preparecomposite electrode with excellent cycling performance,which is consistent with that of CV curves.

ConclusionsWe demonstrated preparation of flexible and self-supporting PEDOT-PSS/RGO nanocomposite films with alayered structure through a simple vacuum-filteredmethod. The superior capacitive performance of thePEDOT-PSS/RGO nanocomposites was confirmed bythe tests of electrochemical properties. The mass ratioof PS/RG showed distinct influence on electrochemicalperformance of as-prepared composite electrodes. A193.7 F/g highly specific capacitance was achieved at acurrent density of 500 mA/g. Furthermore, comparedwith pure PEDOT-PSS film, this nanocomposite film

exhibited better energy-storage stability and can keep90.6 % of the original specific capacitance after 1000 cycles.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsWY conceived of the study, carried out the fabrication of PEDOT/RGOcomposites, and drafted the manuscript. YC, YZ, and XH helped to depositthe films and analyze the data. YJ and JX helped to develop the idea andguided the study. YY and SL helped to draft the manuscript. All authors readand approved the final manuscript.

Authors’ informationWY, YC, YZ, and XH are students of a doctor’s degree at the School ofOptoelectronic Information, University of Electronic Science and Technologyof China. YY and SL are associate professors at the School of OptoelectronicInformation, University of Electronic Science and Technology of China. JXand YJ are professors at the School of Optoelectronic Information, Universityof Electronic Science and Technology of China.

AcknowledgementsThe work was supported by the National Science Foundation of China (NSFC)(No.51477026 and No.61471085).

Received: 10 April 2015 Accepted: 11 May 2015

References1. Frackowiak E, Béguin F. Carbon materials for the electrochemical storage of

energy in capacitors. Carbon. 2001;39:937–50.2. Burke A. Ultracapacitors why, how, and where is the technology. J Power

Sources. 2000;91:37–50.3. Snook GA, Kao P, Best AS. Conducting polymer based supercapacitor

devices and electrodes. J Power Sources. 2011;196:1–12.4. Yoon SB, Kim KB. Effect of poly(3,4-ethylenedioxythiophene) (PEDOT) on the

pseudocapacitive properties of manganese oxide (MnO2) in the PEDOT-MnO2-multiwall carbon nanotube (MWNT) composite. Electrochim Acta.2013;106:135–42.

5. Obreja VN. On the performance of supercapacitors with electrodes basedon carbon nanotubes and carbon activated material—a review. Physica E.2008;40:2596–605.

6. Sonia TS, Mini PA, Nandhini R, Sujith K, Avinash B, Nair SV, et al. Compositesupercapacitor electrodes made of activated carbon-PEDOT-PSS and activatedcarbon-doped PEDOT. B Mater Sci. 2013;36:547–51.

7. Yang YJ, Zhang LN, Li SB, Yang WY, Xu JH, Jiang YD, et al. Electrochemicalperformance of conducting polymer and its nanocomposites prepared bychemical vapor phase polymerization method. J Mater Sci-Mater EL.2013;24:2245–53.

8. Han YQ, Shen MX, Wu Y, Zhu JJ, Ding B, Tong H, et al. Preparation andelectrochemical performances of PEDOT/sulfonic acid-functionalizedgraphene composite hydrogel. Synthetic Met. 2013;172:21–7.

9. Sun D, Jin L, Chen Y, Zhang JR, Zhu JJ. Microwave-Assisted in situ synthesisof Graphene/PEDOT hybrid and its application in supercapacitors. ChemPlus Chem. 2013;78:227–34.

10. Yang YJ, Yang XJ, Yang WY, Li SB, Xu JH, Jiang YD. Ordered and ultrathinreduced graphene oxide LB films as hole injection layers for organiclight-emitting diode. Nanoscale Res Lett. 2014;9:537.

11. Yang SL, Deng BC, Ge RJ, Zhang L, Wang H, Zhang ZH, et al. Electrodepositionof porous graphene networks on Nickel foams as supercapacitor electrodeswith high capacitance and remarkable cyclic stability. Nanoscale Res Lett.2014;9:672.

12. Österholm A, Lindfors T, Kauppila J, Damlin P, Kvarnström C. Electrochemicalincorporation of graphene oxide into conducting polymer films.Electrochim Acta. 2012;83:463–70.

13. Han YQ, Ding B, Tong H, Zhang XG. Capacitance properties of graphiteoxide Poly(3,4-ethylene dioxythiophene) composites. J Appl Polym Sci.2011;121:892–8.

14. Yang WY, Xu JH, Yang YJ, Chen Y, Zhao YT, Li SB, et al. Porous conductingpolymer and reduced graphene oxide preparation, characterization andelectrochemical performance. J Mater Sci-Mater EL. 2015;26:1668–77.

Yang et al. Nanoscale Research Letters (2015) 10:222 Page 7 of 7

15. Lim K, Jung S, Lee S, Heo J, Park J, Kang JW, et al. The enhancement ofelectrical and optical properties of PEDOT:PSS using one-step dynamic etchingfor flexible application. Org Electron. 2014;15:1845–55.

16. Yang Q, Pang SK, Yung KC. Study of PEDOT–PSS in Carbon nanotube/conducting polymer composites as supercapacitor electrodes in aqueoussolution. J Electroanal Chem. 2014;728:140–7.

17. Antiohos D, Folkes G, Sherrell P, Ashraf S, Wallace G, Aitchison P, et al.Compositional effects of PEDOT-PSS/single walled Carbon nanotube filmson supercapacitor device performance. J Mater Chem. 2011;21:15987–94.

18. Hummers WS, Offeman RE. Preparation of graphitic oxide. J Am Chem Soc.1958;80:1339.

19. Rajagopalan B, Chung JS. Reduced chemically modified graphene oxide forsupercapacitor electrode. Nanoscale Res Lett. 2014;9:535.

20. Wu Q, Xu YX, Yao ZY, Liu A, Shi GQ. Supercapacitors based on flexibleGraphene/Polyaniline nanofiber composite films. ACS Nano. 2010;4:1963–70.

21. Dikin DA, Stankovich S, Zimney EJ, Piner RD, Dommett GHB, Evmenenko G,et al. Preparation and characterization of graphene oxide paper. Nature.2007;448:457–60.

22. Chen HQ, Müller MB, Gilmore KJ, Wallace GG, Li D. Mechanically strong,electrically conductive, and biocompatible graphene paper. Adv Mater.2008;20:3557–61.

23. Zhang JT, Zhao XS. Conducting polymers directly coated on reducedgraphene oxide sheets as high-Performance supercapacitor electrodes.J Phys Chem C. 2012;116:5420–6.

24. Wan L, Wang B, Wang SM, Wang XB, Guo ZG, Dong BH, et al. Well-dispersedPEDOT:PSS/graphene nanocomposites synthesized by in situ polymerization ascounter electrodes for dye-sensitized solar cells. J Mater Sci. 2015;50:2148–57.

25. Elya F, Matsumoto A, Zoetebiera B, Peressinotto VS, Hirata MK, Sousa DA,et al. Handheld and automated ultrasonic spray deposition of conductivePEDOT:PSS films and their application in AC EL devices. Org Electron.2014;15:1062–70.

26. Weng YT, Wu NL. High-performance poly(3,4-ethylene-dioxythiophene)-polystyrenesulfonate conducting-polymer supercapacitor containing hetero-dimensional carbon additives. J Power Sources. 2013;238:69–73.

27. Chu CY, Tsai JT, Sun CL. Synthesis of PEDOT-modified graphene compositematerials as flexible electrodes for energy storage and conversion applications.Int J Hydrogen Energy. 2012;37:13880–6.

28. Xu YF, Wang Y, Liang JJ, Huang Y, Ma YF, Wan XJ, et al. A hybrid material ofgraphene and poly (3,4-ethyldioxythiophene) with high conductivity,flexibility, and transparency. Nano Res. 2009;2:343–8.

29. Zhou H, Yao W, Li G, Wang J, Lu Y. Graphene/poly(3,4-ethylenedioxythiophene) hydrogel with excellent mechanical performanceand high conductivity. Carbon. 2013;59:495–502.

30. Yan D, Liu Y, Li YH, Zhuo RF, Wu ZG, Ren PY, et al. Synthesis andelectrochemical properties of MnO2/rGO/PEDOT:PSS ternary compositeelectrode material for supercapacitors. Mater Let. 2014;127:53–5.

31. Tai Z, Yan X, Lang J, Xue Q. Enhancement of capacitance performance offlexible Carbon nanofiber paper by adding graphene nanosheets. J PowerSources. 2012;199:373–8.

32. Zhang LL, Zhao SY, Tian XN, Zhao XS. Layered graphene oxidenanostructures with sandwiched conducting polymers. Langmuir.2010;26:17624–8.

33. Lu XJ, Dou H, Yuan CZ, Yang SD, Hao L, Zhang F, et al. Polypyrrole carbonnanotube nanocomposite enhanced the electrochemical capacitance offlexible graphene film for supercapacitors. J Power Sources. 2012;197:319–24.

Submit your manuscript to a journal and benefi t from:

7 Convenient online submission

7 Rigorous peer review

7 Immediate publication on acceptance

7 Open access: articles freely available online

7 High visibility within the fi eld

7 Retaining the copyright to your article

Submit your next manuscript at 7 springeropen.com